I would like to make my lil bambino some wool diaper covers (soakers/shorties/longies/wraps) and I plan on buying the wool by the yard. Do I prep the wool in any way before sewing it? Will it shrink at all if I wash by hand?

If you're buying wool interlock that is "feltable" then you will want to felt it up by washing and drying it. Usually it shrinks by about 1/3. This makes it much nicer/thicker/squishier. It will still be plenty stretchy but will function better after you felt it.

__________________
Catholic wife to the very best hubby in the world and mama to five boys:
John-Paul, William, Oliver, Teddy , and with no name yet.